1. Field of the Invention
This invention relates to a so-called serial printer that prints by moving the print head relative to the recording medium. In particular, the present invention relates to a technique of preventing a loss of print data when the print head does not move correctly. Therefore, the present invention relates to a technology that is strongly related to printers used in systems that handle monetary data, such as POS/ECR.
2. Description of the Related Art
Because of its structure, a serial printer needs to know the position of the print head. This is because without knowing the current print head position, the printer is unable to print accurately at a given position even when a print position on the recording medium is specified. In this sense, the printer also needs to know the position at which the recording medium is mounted.
In order to set the print head at its initial position, a conventional serial printer moves the print head in a specified direction until the print head is detected by the print head reference position detector. Because the reference position detector normally is provided at one end of the printable area, the direction of motion is uniquely determined as the direction from the current position of the print head toward the reference position detector. If a reference position is not detected even when the drive motor is operated to an extent equivalent to the amount of motion of the print head corresponding to the width of the printable area, the printer determines that the print head cannot be set at its initial position, and terminates processing by stopping the carriage motor. Incidentally, the process or operation of setting the print head at its initial position is referred to as the initialization of the print head, or, simply, as initialization.
Serial printers are used as output terminals for various information-processing devices. In particular, they are often used in systems that are involved in handling of money, such as POS/ECR systems. Confirming the details of transactions in writing is deep-rooted in the customary use of these systems, and transaction data is always printed. Therefore, for handling monetary transactions using such a system, the results of printing are critical; in such a system, the accuracy and reliability of print results are of paramount importance.
The information-processing devices and associated printers discussed above are normally used by operators of varying skill levels. Therefore, it is important that the printer be able to print reliably, regardless of the operator. With a printer, an especially important requirement is the absence of printing malfunction that could lead to a loss of print data.
In the conventional initialization operation discussed above, it is possible to determine whether or not the moving operation was performed correctly by moving the print head from the current position to the reference position and by setting the print head at the reference position. In other words, if the reference position is not detected during the above initialization operation, it is possible to infer that moving of the print head to the reference position was not performed correctly due to some kind of error.
The range in which the print head is moved by this processing, however, does not necessarily encompass the entire area in which the print head can print. Therefore, the initialization processing cannot detect error conditions in the entire area. In other words, even if the initialization operation has normally terminated, problems could exist in the parts of the print area through which the print head did not pass. These problems include a protruding recording medium in the path of print head motion, the presence of foreign objects, or an error in the print head transport mechanism. Conventional methods cannot detect these problems.
Therefore, conventionally it is possible that printing is performed even if such a print hindering condition exists. In such a case, the print data which the printer has received from the information-processing equipment is liable to be erased from the printer before it can be printed in a form amenable to visual inspection. This can be a serious problem especially in POS/ECR systems involved in handling of money.